How does video on demand work? - Canadian TV, Computing and Home Theatre Forums
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post #1 of 17 (permalink) Old 2006-09-05, 12:46 PM Thread Starter
 
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How does video on demand work?

I got the new receiver and received a 100$ credit for the 900 channel. So I decided to use it and watched the black and white show by Gregory Charles. Really good show by the way.

But it got me thinking. How can they have the bandwidth for that? It's not like the channels where you order a movie and must watch it at the time where it is shown. This starts anytime you want, you can pause it. Stop it and go back to it later.

Do they really have all that extra bandwidth? Or is it some other technology that I am not aware of. I try to think of how much time it would take my cable modem to download a 2hrs+ HDTV program.. probably many days. And it's instantaneous with this. I was even able to FFWD right from the start, no download or buffering time!
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post #2 of 17 (permalink) Old 2006-09-05, 04:27 PM
 
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Without entering in technical term, you just simply watch it directly on the server. The server broadcast the emission on a frequency that you syntonize with the 900.
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post #3 of 17 (permalink) Old 2006-09-05, 08:01 PM Thread Starter
 
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Originally Posted by SyStEm[666] View Post
Without entering in technical term, you just simply watch it directly on the server. The server broadcast the emission on a frequency that you syntonize with the 900.
Please get into technical terms. I work with computers so I'm not totally ignorant of technology. In fact I was working for Videotron Internet as a consultant abut 10 years ago.

I'm wondering how can I be watching that show at the same time as someone else if it's broadcast on channel 900. Other people won't be at the same time in the show as where I am. I can pause and resume whenever I want. Unless there is a LOT of available bandwidth and 900 is just a "placeholder" for wherever the show is brodcast for me specifically.
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post #4 of 17 (permalink) Old 2006-09-05, 09:42 PM
 
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Each video channel is allocated a certain amount of bandwidth (I think 6 Mhz which is about 60 Mbps)
There is some reserved "channels" that are used for various other purposes.
One of those is internet where there is a dedicated channel that is broken up into timeslots where different users on the same cable can send upstream to the cable company. Then several channels are used for the download. That is why your uplink is much less then your downlink. There are also several channels reserved for VOD with the same concept as above.

When you get past the channel layer it is basically TCP/IP. Therefore you can broadcast to everyone or send to a specific MAC or IP address of your Illico box.
On each cable link there is a maximum amount of people that can get a VOD but I suppose Videotron does a best guess and determines what is the amount of channels they want to reserve for VOD and how many maximum people they expect at any one time.
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post #5 of 17 (permalink) Old 2006-09-06, 02:39 PM
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Quote:
Do they really have all that extra bandwidth?
No, every VOD program ordered is not being broadcast to every home.

From what I understand VOD is just IPTV and the program is being streamed from a VOD file server at the cable company to your set top box.

Really no different than watching a file from the internet over your cable high speed internet connection except the file is being streamed to your set top box and not your computer.



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post #6 of 17 (permalink) Old 2006-09-06, 02:50 PM
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I believe there is also some "smart technology" used so that the people on a certain node, only get the programming they "need", not what's required "everywhere" on the system.

I believe on Rogers this is typically where the fibre ends and the copper takes over.

I believe they will also be introducing similar technlogy so that all digital channels are not sent to all homes at all times, only the watched channels (on a node).

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post #7 of 17 (permalink) Old 2006-09-06, 06:04 PM
 
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From what I've heard, you can have about 40 people watching VOD in an area. (Basicaly, 1000 person by area)

By I dunno if that change because that what I've heard 8 month ago when I joined Videotron
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post #8 of 17 (permalink) Old 2006-09-06, 10:57 PM
 
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What I said was "When you get past the channel layer it is basically TCP/IP. Therefore you can broadcast to everyone or send to a specific MAC or IP address of your Illico box."

The VOD is sent to everyone on the cable link however only your illico box will be able to receive it since it is addressed to your MAC or IP.
This is the same concept as ethernet.. everyone sees it but only the intended recipient will listen to it. (In fact when you download a file from the internet using cable high speed internet service every cable modem on your cable link sees the traffic just your cable modem responds)

Since there are region and area hubs that run fiber as far as possible to the end user bandwidth is not an issue until the "last mile" where cable begins. Therefore at the headoffice the CMTS (cable modem termination) can send the VOD to the right area. Then a device that converts fiber to cable determines which cable link to send the VOD to. Therefore the fiber to your area and only your cable link contains the VOD.
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post #9 of 17 (permalink) Old 2006-09-07, 12:37 AM
 
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Quote:
Originally Posted by Fastfwd View Post
Please get into technical terms. I work with computers so I'm not totally ignorant of technology. In fact I was working for Videotron Internet as a consultant abut 10 years ago.
VOD command are broadcasted exactly the same way as standard digital channel, meaning by QAM of 6 Mhz. 4 QAMs are reserved for this (only 3 in some region). One QAM can broadcast 38.8 Mbps (which is about 37.5 Mbps for the "real" data). Videotron encoded all there VOD stuff with a fix bitrate of 3.3 to 3.5 Mbps. Audio could be in 192 Kbps or 384 Kbps, which mean that the video bitrate is about 3.1 to 3.3 Mbps. 10 VODs command could be broadcast in the same time, within one QAM. So, it's 30 to 40 shows by "cell" (around 1000 doors).

When you looking at channel 900, it only start a software to let you choose what you want to see. When you order something, I don't know if the show is already in the hard drives of your local neighbourhood station but, anyway, it's connected by fiber optic, so, the time is very short before the show start. At this time, your terminal received the information about which QAM to tune and which program (numeric number) to watch. If you look at the page 1 of your status menu, when you are watching a VOD, you will see the frequency tuned by your terminal for this command. Before the show start, it's completly copied in your local station, on hard drive. So, you have full control over the broadcast, for one day. If you do nothing for more than 15 minutes, the program slot is freed for other VOD programs. If all the VOD programs slots are busy, you will get a error code but this is really rare.

By the way, there is some HD show now. They seemd to be encoded to take the place are 4 SD programs.

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post #10 of 17 (permalink) Old 2006-09-07, 07:30 AM
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Thanks to all who posted. Some interesting stuff on this thread.



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post #11 of 17 (permalink) Old 2006-09-07, 09:04 AM
 
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Yes, this has been very interesting and educational as well.
When I first got VOD I used to get an error 4 times out of 5. When I called my cable company they said that there were too many users at the moment and to try again later.... I have not had this problem in over a year.. so something has changed... for the better.

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post #12 of 17 (permalink) Old 2006-09-07, 07:45 PM
 
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As I walk around my suburban neighborhood, I see large Videotron boxes on telephone poles half the size of a refrigerator. These are a recent addition in the last 5 years.

I would hazard a guess that each of these boxes contains a video jukebox of every film under the 900 menu and that is how it is so easy to provide VOD to a small number of subscribers in any one area who might need this service without trashing the bandwidth.

Montreal
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post #13 of 17 (permalink) Old 2006-09-08, 12:46 AM
 
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Nope, those are batteries for backup for telephone.

All the server are in the same place where you get your signal from. So basically for Montréal, it's at 150 beaubien :P
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post #14 of 17 (permalink) Old 2006-09-08, 09:21 AM
 
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Quote:
Originally Posted by SyStEm[666] View Post
Nope, those are batteries for backup for telephone.
Thanks for enlightening me.

I thought that part of those boxes were refrigerators to keep drinks cold for the technicians.

Montreal
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post #15 of 17 (permalink) Old 2006-09-08, 10:59 AM
 
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I agree, very interesting thread. I had the same questions when I watched Gregory Charles Black and White on HD last weekend. The sound and the video was incredible. I wondered what was the bandwidth I used, and what is the maximum number of people that can order this show at the same time (especially since they do sort of advertise it a lot recently). I wish I tought about looking into the status page.
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